Wafer inspection systems help a semiconductor manufacturer increase and maintain integrated circuit (IC) chip yields by detecting defects that occur during the manufacturing process. One purpose of inspection systems is to monitor whether a manufacturing process meets specifications. The system indicates the problem and/or the source of the problem if the manufacturing process is outside the scope of established norms, which the semiconductor manufacturer can then address.
Defect detection sensitivity and throughput are coupled in inspection systems such that greater sensitivity usually means lower throughput. There are both physical and economic reasons for this relationship. Semiconductor manufacturers demand improved sensitivity from inspection systems, but require a minimum throughput.
Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.
In IC manufacturing, patterns sensitive to photolithography are called “litho hotspots” (“hotspots” for short). Hotspots can be formed during manufacturing or by interactions between manufacturing process steps. For example, a certain feature may be difficult to fill, so this is a place where an open can occur. Thus, the feature may have printed correctly, but did not fill correctly. As feature sizes shrink in advanced technology nodes, the number of hotspots increases. Inspection of hotspots can be challenging because hotspots are small. For example, hotspots can be on the order of 10 nm.
Previous techniques to inspect hotspots involved an image time of less than 10 ms, but the overhead of stage moving, settling, aligning, and focusing was usually about 150 ms to 200 ms. Therefore, the effectiveness of the inspection was very low because approximately 95% of operation time was overhead and only approximately 5% of operation time was actually running inspection.
Therefore, what is needed is improved wafer inspection using a charged particle beam system.